Methods and Systems for Dredging

ABSTRACT

The invention relates to a dredging method for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel. The method comprises performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel, the collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel. The method also comprises, in a step different from said performing agitation dredging, after solidification of the sediment collected in the collector, removing the solidified sediment from the collector so that the collector again has a bottom level positioned substantially deeper than the nautical depth of the navigation channel.

FIELD OF THE INVENTION

The invention relates to the field of agitation dredging in general and in particular water injection dredging. The present invention relates to methods and systems for performing, monitoring, controlling and/or optimizing the agitation dredging process to liquefy, erode and displace sediment in a port or waterway towards a central collector and optionally remove the sediment with alternative methods from the collector. This may optimize the dredging effort.

BACKGROUND OF THE INVENTION

Transport over water is becoming more and more important in a globalized economy. This results in more and bigger vessels and ships that need to enter harbors and inland waterways. Therefore the navigability of harbors and waterways need to be guaranteed. Deepening and widening of waterways and harbors is a constant activity done by authorities to ensure ships can pass and navigate. In most of the ports and waterways there is also continuous inflow of sediments and therefore maintenance dredging is necessary. To determine when and how much there needs to be dredged the underwater sediment and mud layers must be monitored and analyzed. Classically the maintenance dredging work is performed by trailer suction hopper dredgers, but alternatively the same result can be achieved by WID (water injection dredging) dredgers in combination with supportive techniques.

If a similar result can be achieved by agitation dredging like by WID dredgers the resulting effort and cost can be reduced.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for dredging, e.g. agitation dredging.

It is an advantage of at least some embodiments of the present invention in that they provide in a combined method of an agitation dredging technique and a sediment collector, a water injection platform system, a method or system for assisting in such a dredging method or a mat that can be used in such a dredging method.

The above object can be obtained using methods, systems or products according to embodiments of the present invention.

In one aspect, the present invention relates to a method for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel, the method comprising

performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel, the collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel,

in a step different from said performing agitation dredging, after solidification of the sediment collected in the collector, removing the solidified sediment from the collector so that the collector again has a bottom level positioned substantially deeper than the nautical depth of the navigation channel.

It is an advantage of embodiments of the present invention that the action of mobilizing and the action of removing collected sediment from the navigation channel is decoupled, allowing to use different means for the mobilizing and the removing.

It is an advantage of embodiments of the present invention that the action of removing sediment from the collector can be performed less frequent, e.g. using a larger dredger, by temporary storing sediment in a local collector.

Displacing the mobilized sediment may be performed by water injection. The displacement of the mobilized sediment can be over a distance of up to several tens of meter. In a special case the action of the movement of sediment can be assisted by a plough dredger. The plough dredger can assist in driving sediment to the collector.

The method may comprise, prior to said agitation dredging, forming the trench in the navigation channel. It is an advantage of embodiments of the present invention that a natural collector can be used. Alternatively, an artificial collector, such as for example made of concrete walls can be created in the navigation channel having a floor positioned substantially below the nautical depth.

Said performing agitation may comprise agitation dredging through water injection dredging using a water injection dredger.

Said performing agitation may comprise using a water injection system installed at or near the nautical bottom.

Said performing agitation may comprise performing agitation through a water injection system being at least partly integrated in mats for scour protecting or mats forming the wall of the collector.

Said removing sediment from the collector may comprise removing sediment with a jumbo hopper dredger. Said removing sediment from the collector may comprise removing sediment by pumping through a stationary or mobile pumping system.

The method may comprise, prior to said performing agitation for mobilizing sediment, determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer.

The method may comprise predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical depth.

The present invention also relates to a method for assisting a dredging process in a navigation channel, the dredging process comprising a step of performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector in the navigation channel and a separate step of removing sediment from the collector, wherein the method for assisting comprises

determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer, and/or

predicting when the sediment needs to be removed from the collector. Said predicting may be based on an estimate of the amount of mobilized sediment collected in the collector. Determining dredging parameters or determining when the sediment needs to be removed may be determined based on the nautical depth, a consolidation level of the sediment, the amount of sediment in the collector, . . . etc.

The present invention also relates to a water injection platform for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel, the platform comprising an agitation system for performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel, the collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel.

The platform further may comprise the collector for collecting the mobilized mud.

The platform may comprise a dredging pumping system for pumping the liquefied sediment or for collecting the sediment from the collector.

The collector may be a trench made in the seabed of the navigation channel.

The agitation system may be based on a floating platform or vessel.

The water injection system may comprise a submersed system with mounted or integrated nozzles.

The water injection system may comprise one or more mats where injectors are integrated and connected with a water injection pump. The mat may be a mat suitable for scour protection or as surface or wall to shape a collector.

The collector may be formed and shaped in the soil or in the mud.

The collector may be made out of material like concrete or steel.

The water injection platform may furthermore comprise a monitor system for measuring soil strength and density for determining the dredging power, the dredging effort in hours and the water injection volume to erode, liquefy and mobilise an underwater sediment layer.

The water injection platform may comprise a monitor system for predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical depth or consolidation level or density level in the collector.

The water injection platform may comprise a pumping station on a dredging ship for pumping the sediment from the collector towards a dredging ship or a stationary pumping station for pumping the sediment from the collector towards a pipe line to relocate the sediment to a dumping or treatment site where the sediment is permanently stored or where it is re-suspended and carried away from the area temporally or permanently.

The present invention also relates to a monitor system for assisting a dredging process in a navigation channel, the dredging process comprising a step of performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel and a separate step of, after solidification of the sediment collected in the collector, removing the solidified sediment from the collector so that the collector again has a bottom level positioned substantially deeper than the nautical depth of the navigation channel, the monitoring system being adapted for determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer, and/or for predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical bottom level or consolidation level or density level in the collector.

The monitoring system may be adapted for predicting when the sediment needs to be removed from the collector based on an estimate of the amount of mobilized sediment collected in the collector and or the consolidation or density levels of the sediment in the collector.

The present invention also relates to a mat for protecting or forming a bottom for a navigation channel, the mat comprising a fluid delivery system, such as for example an integrated or mounted injectors, for injecting water for mobilizing sediment that has formed on the mat.

The injectors may be integrated in the mat, the injectors being part of or integrated in a fluidic channel system.

The injectors may be positioned at one end of the channels of the fluidic channel system and wherein the channels are at the other end are combined and form a water injection entrance.

The injectors may be oriented in a predetermined direction away from perpendicular to the mat surface in order to displace the sediment along a given direction.

The mat may be a mat suitable for scour protection or as surface or wall to shape a collector.

The collector can act as a buffer where agitated and mobile sediment can consolidate and be removed by different techniques like a static or dynamic pump station or by a hopper dredger. The collector can be shaped in this way that the liquefied and mobilized sediment can flow towards a collection area. The angle of repose of a sediment is reduced while the pore pressure of the sediment is being increased to the point the sediment becomes a liquefied substance or thixotropic substance and is being mobilized by means of induced or natural currents or slope induced gravity to a designated area or reservoir of collection called collector where the sediment either is stored for relatively short periods or consolidates to be collected at a later stage.

The collector can be .e.g. a central trench where the slopes are under a sudden angle towards the trench induce to induce sediment flowing towards the trench. The collector can also be a network of trenches. The trenches can be natural or preinstalled with a hopper dredger or by a plough dredger and or in combination with water injection dredging, and are typically deeper than the nautical depth of the port or waterway. Due to the fact that the trenches are deeper than the nautical depth, they act as a buffer location in space and time for liquefied sediment.

The sediment is then being pumped out by means of a pumping station, this pumping station can be a dredging ship or in the case the sediment remains in suspension in the collector a permanent installation and a pipe line to relocate the sediment to a dumping or treatment site where the sediment is permanently stored or re-suspended and carried away from the area temporally or permanently.

The sediment in suspension can be further threated. Treatments of the suspension can be degassing in order to increase the bulk density of the suspension and to let it stay low in the water column. Treatments of the suspension can be adding micro or larger gas bubbles into the suspension to oxidize the sediment particles or to decrease the bulk density of the suspension in order to let the suspension move upward in the water column. Treatments can be the dewatering of the sediment suspension in order to increase bulk density or increase the yield point of the sediment suspension. Treatments can be dilution of the sediment in order to decrease bulk density or decrease the yield point of the sediment suspension.

The liquefaction of sediment layers in e.g. a shipping channel comprises the injection of high volumes of water into the sediment at relatively low pressures. The water volume can either be injected from above the sediment by a water injection dredger or from below the sediment by permanent infrastructure placed at or below maintenance depth before the sediment settled down and formed a sediment layer.

Typically sediment is being diluted to the point where all solid properties of the sediment are lost and the suspended sediment can be described as a fluid. Typically the injection volume of additional water into the sediment is about a factor 0.25 to 3 higher than the volume of sediment to be mobilized, depending on the initial bulk density of the sediment and the yield characteristics of the sediment or sediment suspension.

The designated area of the collector where sediment accumulation and or consolidation is possible is a buffer where the re-suspended sediment is prevented to flow back into the dredged area. Current measurements and models are often required to determine the optimum time interval where further transport and re-suspension can occur.

The time interval where the suspended sediment is buffered before being transported can be extended by increasing the suspended sediment layer thickness. Consolidation invokes an upward going drainage current, hence the effect is similar to artificial water injection into the sediment: the upper layer of the sediment remains in suspension until the water current drops below a critical discharge. This effect allows intertidal buffering of the suspended sediment with a minor penalty of sediment that will remain consolidated on the bottom of the reservoir.

When consolidation speed is to be increased additions to the sediment can be made. A silt and or clay mixture can be mixed up with sand particles in order to increase consolidation speed. In a tidal area gas bubbles can also be added to the suspension in order to have a natural pumping effect based on the increase and decrease of the bubble volume in function of the change of hydrostatic pressure, following the universal gas law V=nrT/P. The bubble oscillation will pump additional water through the sediment drain channels and as such enhance the sediment consolidation speed.

When consolidation speed is to be decreased extractions from the sediment can be made. A sand fraction can be extracted in order to decrease consolidation speed. In a tidal area gas bubbles can also be extracted from the suspension in order to decrease the natural pumping effect based on the increase and decrease of the bubble volume in function of the change of hydrostatic pressure, following the universal gas law V=nrT/P. A reduction of the bubble oscillation will reduce pumping of additional water through the sediment drain channels and as such decrease the sediment consolidation speed.

In order to determine if the sediment can be eroded by water injection dredging, soil strength, soil rheological parameters and soil density parameters need be measured. An example of a soil strength measurement instrument is a free fall penetrometer where the intrusion resistance is a measure for the strength of the soil. The soil strength is in relation with the water injection power to erode a sediment layer.

In order to determine how much water needs to be added to liquefy the sediment and make it Newtonian or quasi-Newtonian, the density of the sediment layer before the injection dredging action needs to be measured.

The combination of strength and density measurement allows to exactly determine the dredging power and dredging time to erode, liquefy and mobilize a sudden mud volume.

Besides the preparation and planning of the dredging operations both measurement methods can also be used to follow up the status of the liquefied suspension in the collector.

Permanent or non-permanent water injection into the sediment can hold the sediment longer into suspension if longer time intervals is a requirement. When water injection dredging is applied the sediment is liquefied and potentially suspended in the water column. The sediment load in the water column can be measured and traced by turbidity sensors. E.g. local measurements with acoustic Doppler current profilers (ADCP) or optical turbidity sensor can show how and in which direction the mobilized mud is moving. The turbidity sensor can be installed on an autonomous vessel to follow from the surface the underwater sediment flow.

It is an advantage of embodiments according to the present invention that systems and methods are provided for controlling WID dredging actions by installing an underwater collector structure. It is an advantage of embodiments according to the present invention that a natural gravity flow is induced by such a collector.

It is an advantage of embodiments according to the present invention that the mud collector can be made of another material then sediment e.g. concrete or metal.

It is an advantage of embodiments according to the present invention that the on the mud collector injection nozzles are mounted.

It is an advantage of embodiments according to the present invention that the on the mud collector injection nozzles are mounted on the collector structure and that the injection nozzles are driven by a tidal pump system.

It is an advantage of embodiments according to the present invention that scour protection mats are used as injection systems where tubes and operating in the mats are functioning as injector. By pumping water in the mats.

It is an advantage of embodiments according to the present invention that scour protection mats are used as collector surface.

It is an advantage of embodiments according to the present invention that scour protection mats are combined with water injection nozzles which are mounted on or in the mat and driven by tidal pumps.

It is an advantage of embodiments according to the present invention that systems and methods are provided to generate and shape the collector in the mud layer. The collector can be shaped by a HTSD or WID dredger or a plough dredger.

It is an advantage of embodiments according to the present invention that systems and methods are provided to combine the collector with a pump station. The pump station will suck the liquefied sediment out of the collector and will transport it to a dumping site. The pump station can be stationary and connected to a quay wall or can be mobile and mounted on a floating platform.

It is an advantage of embodiments according to the present invention that systems and methods are provided to combine the pump station with a pipe lines or pipe floats to pump the sediment outside a dock or waterway into the open water.

It is an advantage of embodiments of the present invention that methods and systems are provided for analyzing the physical soil parameters like tip and shear strength of a free fall cone to determine the WID dredging power and effort.

It is an advantage of embodiments of the present invention that methods and systems are provided for analyzing the physical soil parameters like density of the sediment layer to determine the gel point of the sediment and liquefying effort.

It is an advantage of embodiments of the present invention that methods and systems are provided for analyzing the turbidity to determine in which direction the liquefied sediment cloud is directed. The turbidity can be analyzed by a turbidity sensor is mounted on an unmanned surface vessel that is autonomous tracing the sediment cloud.

It is an advantage of embodiments according to the present invention that parameter such as required dredging power for dredging the different soil layers can be derived, as well as the nautical bottom of the waterway, the soil structure and the identification of the soil type and that this information is used to optimize the dredging effort.

The above objective is accomplished by a method and device according to the present invention.

The present invention relates to a computerized system for obtaining information regarding the related parameters of the water injection dredging process and the status of the collector, the system comprising an input means from sensors, for example sensors on a WID or plough dredger, sensors in the navigation way, such as in or near the collector, in or near mats in the navigation way, sensors in probing systems, penetrometers, etc. Typically a processor is provided for determining the relevant information. Information regarding the shape, size or other features of the collector also may be used.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of an water injection dredger as can be used in embodiments of the present invention.

FIG. 2 shows a T-bar with injection nozzles as can be used in embodiments of the present invention.

FIG. 3 shows the injection dredging principle where sediment is injected, liquefied, mobilized and displaced, according to an embodiment of the present invention.

FIG. 4 shows the water injection principle in combination with a trench. The trench is cut out of the seabed. The water injection dredging technique is used to erode and mobilize sediment from around the trench into the trench, according to an embodiment of the present invention.

FIG. 5 show a cross section of a navigation channel where the seabed soil underwater is depicted, before applying a method according to an embodiment of the present invention.

FIG. 6 shows a navigation channel where in the middle of the channel a trench is made, according to an embodiment of the present invention.

FIG. 7 shows a figure where the sediment in the navigation channel is mobilized from the side into the trench, according to an embodiment of the present invention.

FIG. 8 illustrates the working procedure according to an embodiment of the present invention, wherein the erosion is done in steps starting from close to the trench going to the other sides. While mobilizing the sediment a small slope is introduced.

FIG. 9 shows a filled trench with water sediment emulsion as can be obtained using a method according to an embodiment of the present invention. The trench is used to consolidate the sediment.

FIG. 10. Illustrates features and principles as can be used for determining the liquid delivery system parameters in mats usable in embodiments of the present invention.

FIG. 11 to FIG. 14 illustrate features and principles as can be used in methods and systems for monitoring or assisting in dredging methods according to embodiments of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In the following detailed description, specific details are set forth in order to provide a thorough understanding of the invention and how it may be practiced in particular embodiments. However it will be understood that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures and techniques have not been described in detail, so as not to obscure the present invention. While the present invention will be described with respect to particular embodiments and with reference to certain drawings, the reference is not limited hereto. The drawings included and described herein are schematic and are not limiting the scope of the invention. It is also noted that in the drawings, the size of some elements may be exaggerated and, therefore, not drawn to scale for illustrative purposes.

Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

It is to be understood that the terms used in embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.

It is to be understood that the term “comprising” should not be interpreted as being restricted to the steps or elements listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising A and B” should not be limited to devices consisting only of components A and B.

Where in embodiments according to the present invention reference is made to a waterway, reference is made to a navigable body of water, such as a river, channel, canal, sea, lake or ocean.

Where in embodiments according to the present invention reference is made to agitation dredging type identification, reference is made to water injection dredging of the soil based on injection of the top layer of the soil, eroding, liquefying and displacing the top layer of the soil consisting of sediment. This dredging technique can be combined with plough dredging to help moving mechanically the soft sediment.

Where in embodiments according to the present invention reference is made to “nautical depth”, reference is made to the depth where physical characteristics of the bottom of a waterway reach a critical limit beyond which normal navigation is not possible. The nautical bottom can be defined as the level where physical characteristics of the bottom reach a critical limit beyond which contact with a ship's keel influences the controllability and maneuverability. According to embodiments of the present invention, the nautical depth may be defined as in the report Navigation in muddy areas, Supplement to Bulletin no. 43, PTC2 report of WG 03-1983 issue, MarCom Working Group 03.

Where in embodiments according to the present invention reference is made to “soil structure” and “soil type” or “soil type identification”, reference is made to the classification of the soil type based on the physical parameters of the measured soil. Based on for example the density, shear stress, viscosity and other physical parameters a soil type can be identified.

Where in embodiments according to the present invention reference is made to a soil type identification, reference is made to the classification of the soil type based on the physical parameters of the measured soil.

In a first aspect, the present invention relates to a dredging method for displacing sediment in a navigation channel towards a deeper collector in order to keep the navigation channel on a sudden depth. According to embodiments of the present invention, a method is described for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel. The method comprises performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel. The method also may comprise, in a step different from said performing agitation dredging, removing sediment from the collector. Said displacing the mobilized sediment may be performed by water injection.

By way of illustration some standard and optional steps are described with reference to an exemplary method comprising several steps.

First step is the use of agitation dredging to mobilize sediment from one place to another. In FIG. 7 a navigation channel is depicted where via the method described in FIG. 3 the top of the soil consisting of deposited sediment is eroded, liquefied and displaced. The displacement is established by the injected water after it was eroded. The displacement can take place over several tens of meters.

The second step is to mobilize the sediment from the bed of a navigation channel towards a deeper positioned trench in the navigation channel. In FIG. 8 a deeper trench in the middle of a navigation channel is depicted. By eroding and liquefying the edges around the trench the loose sediment can be moved into the trench. By moving a portion of the sediment a slope for the sediment further away from the trench is created. During this process the water injection dredger can be assisted by a plough dredger.

The third step is to let the mobilized and liquefied sediment consolidate in the trench. The sediment in the trench is liquefied by the added water of the water injection dredger. By collecting the sediment and leave it untouched over time it will start to dewater and consolidate as depicted on FIG. 9.

The fourth step is a method to empty the collector. The emptying of the collector can happen via a pumping system. The pumping system can a stationary pump or a mobile pump or a jumbo hopper dredger.

Instead of applying a water injection dredger to erode and mobilize the sediment on the seabed of the navigation channel an anti-erosion mat with an internal water injection pumping system could be deployed. When sediment is on top of the mat, water can be injected through the mat so the sediment is liquefied and starts to mobilize. When the mat is under a sudden angle of repose the sediment will start to flow toward a lower point like a collector. Such a mat thus may comprise a fluid delivery system, such as for example integrated or mounted injectors for injecting water or a structure for diffusively providing water, whereby the fluid delivery system is adapted for mobilizing sediment that has formed on the mat. When injectors are used, such injectors can be integrated in the mat. Such injectors may be part of or integrated in a fluid channel system. The injectors may for example be positioned at one end of the channels of the fluidic channel system and the channels may be combined at the other end and form a water injection entrance. Such a water injection entrance may for example be interconnected with a pumping system for pumping water through the mats or may be for example be based on tidal flow. The injectors or water openings may be oriented in such a direction with respect to the mat surface, such that a displacement in a given direction can be enforced to the sediment. The mats used may be suitable for scour protection or may serve as a surface or wall to shape a collector. Design of the mats and the fluid delivery therein can be performed taking into account how consolidation of sediment can be prevented. By way of illustration, an illustration of considerations to be taken into account are described below. FIG. 10 depicts consolidation behaviors of 2 different substances. The evolution of the top of the mud in function of the time is depicted. When injecting water from below the volume of water injected must be at least equal to the volume of water drained from the system. The required volume of water must be equal or more than the worst case drain scenario over a time span of 1 tidal cycle, on average 12 h. Also consolidation speed depends on the mud layer thickness. In order to find the worst case requirements a sample must be taken in-situ, liquidized to the point where yield stress starts to form in the sediment, and a sedimentation column must be filled with sediment until the worst case thickness of the sediment layer that will lay upon the infrastructure. In FIG. 10, the modified mud1 consolidation was 20 cm during one tidal cycle, this would mean that a discharge from below of at least 0.2 m³/m per 12 hours must be done in order to let the sediment recover the drained water. Ideally, the discharge into the sediment layer is at least 2 times higher than the drained volume. The reason why it must be higher is that internal drain channels in the consolidating sediment will also partly drain the injected water and as such reduce the efficiency of the injection. It is expected that the consolidation curve described here is rapid and most sediments in ports will consolidate slower.

The injection of water into the sediment can be done diffuse or by injection nozzles, both systems have advantages and disadvantages. In general one could state that a violent discharge of water into the consolidating sediment will be the most efficient system, since it destroys all internal structures formed during the consolidation. Violent discharge will require nozzles and large volumes of water will need to be available, diffuse injection will require a low discharge rate, minimal water volumes but internal structures in the sediment will be preserved, resulting in a gradual efficiency decrease.

In one aspect, the present invention relates to a water injection platform for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel, the platform comprising an agitation system for performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel. The platform further may comprise the collector. The collector may be a trench in the navigation channel or may be an artificial collector having concrete or metal walls. Furthermore, a dredging pumping system for pumping the liquefied sediment also may be comprised. Other features may correspond with elements of the injection platform used for describing the above method or with means for performing method aspects of the method as described above.

Whereas the mat has been described above as part of an injection platform, the present invention also relates in another aspect to a mat as such, comprising standard and/or optional features as described above.

In yet another aspect the present invention relates to a measurement method for obtaining information regarding the preparation of the dredging method and the follow up of the dredged area and the collector. The present invention thus also relates to a method for assisting a dredging process in a navigation channel, the dredging process comprising a step of performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector in the navigation channel and a separate step of removing sediment from the collector. The method for assisting comprises determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer. Additionally or alternatively the method for assisting comprises predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical depth or a consolidation level or density level in the collector. Such predicting may be based on an estimate of the amount of mobilized sediment collected in the collector. For determining the parameters as described above, use can be made of a free fall penetrometer, such as for example a free fall penetrometer as known from literature. It is to be noticed that for determining the parameters and their use, information may be taken into account regarding the position, shape or other details of the collector in the navigation way. By way of illustration, embodiments of the present invention not being limited thereto, some further details and advantages may be illustrated with reference to FIGS. 11 to 14.

As depicted in FIG. 11 there is a relationship between the cutting depth of the injection nozzle of a WID dredger and the resistance of intrusion of a free fall penetrometer. By taking free fall penetrometer measurements of the sediment layers in the zone of interest, one can predict the cutting depth and the volume of sediment that will be influenced and agitated by the nozzle action.

The bulk density levels of the in-situ sediment determine the amount of water that need to be added in order to bring the sediment to the liquefaction point. As depicted on FIGS. 12, 13 and 14, out of the cutting depth and the density levels the number of times a sudden water injection dredger need to go over measured zone to liquefy and mobilize the measured sediment.

In one aspect, the present invention also relates to a monitoring system for performing a method as described above. Such a monitoring system may be a processing system performing the method steps of the method for assisting dredging as described above, and may include or be connectable to a free fall penetrometer or other parameter determination means for determining parameters. In some embodiments the processing system may also be wireless connectable to such devices for receiving parameter input.

In a further aspect, the present invention relates to a computer program product for, when executing on a computing device, executing the determining and/or deriving of information as described in the method according to the above aspects. The present invention also relates to a computer-readable data carrier storing a computer program product according to this further aspect, and to the transmission of such computer program product over a communication network. The present invention thus also includes a computer program product, e.g. an application program product also referred to as applet, which provides the functionality of any of the data processing steps of the methods according to the present invention when executed on a computing device. The computer program product can also be transmitted via a carrier wave in a network, such as a LAN, a WAN or the Internet. Transmission media can take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications. Transmission media include coaxial cables, copper wire and fibre optics, including the wires that comprise a bus within a computer.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments.

The foregoing description details certain embodiments of the invention. It will be appreciated, however, that no matter how detailed the foregoing appears in text, the invention may be practiced in many ways, and is therefore not limited to the embodiments disclosed. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to include any specific characteristics of the features or aspects of the invention with which that terminology is associated. 

1-30. (canceled)
 31. A method for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel, the method comprising performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel, the collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel, in a step different from said performing agitation dredging, after solidification of the sediment collected in the collector, removing the solidified sediment from the collector so that the collector again has a bottom level positioned substantially deeper than the nautical depth of the navigation channel.
 32. A method according to claim 31, wherein said displacing the mobilized sediment is performed by water injection.
 33. A method according to claim 31, wherein said displacing the mobilized sediment is performed by plough dredging.
 34. A method according to claim 31, wherein, prior to said agitation dredging, the method comprises forming the trench in the navigation channel.
 35. A method according to claim 31, wherein said performing agitation comprises agitation dredging through water injection dredging using a water injection dredger or wherein said performing agitation comprises agitation dredging through water injection dredging using a plough dredger.
 36. A method according to claim 31, wherein said performing agitation comprises using a water injection system installed at or near the nautical bottom.
 37. A method according to claim 36, wherein said performing agitation comprises performing agitation through a water injection system being at least partly integrated in mats for scour protecting or mats forming the wall of the collector.
 38. A method according to claim 31, wherein said removing sediment from the collector comprises removing sediment with a jumbo hopper dredger.
 39. A method according to claim 31, wherein said removing sediment from the collector comprises removing sediment by pumping through a stationary or mobile pumping system.
 40. A method according to claim 31, wherein the method comprises, prior to said performing agitation for mobilizing sediment, determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer.
 41. A method according to claim 31, wherein the method comprises predicting when the sediment needs to be moved to the collector.
 42. A method according to claim 31, wherein the method comprises predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical depth.
 43. A method according to claim 31, wherein the method comprises predicting when the sediment needs to be removed from the collector.
 44. A method for assisting according to claim 43, wherein said predicting is based on an estimate of the amount of mobilized sediment collected in the collector or the degree of consolidation of the sediment in the collector.
 45. A water injection platform for dredging a navigation channel for guaranteeing a nautical depth of a navigation channel, the platform comprising an agitation system for performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector which is embedded in the bottom of the navigation channel, the collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel.
 46. A water injection platform according to claim 45, the platform further comprising the collector for collecting the mobilized mud and/or comprising the platform comprising a dredging pumping system for pumping the liquefied sediment and/or wherein the collector is a trench made in the seabed of the navigation channel and/or wherein the agitation system is based on a floating platform or vessel.
 47. A water injection platform according to claim 45, wherein the water injection system comprises a submersed system with mounted or integrated nozzles and/or comprises one or more mats where injectors are integrated and connected with a water injection pump and/or wherein the mat is a mat suitable for scour protection or as surface or wall to shape a collector and/or wherein the collector is formed and shaped in the soil or in the mud and/or wherein the collector is made out of material like concrete or steel.
 48. A water injection platform according to claim 45, wherein the water injection platform furthermore comprises a monitor system for measuring soil strength and density for determining the dredging power, the dredging effort in hours and the water injection volume to erode, liquefy and mobilise an underwater sediment layer and/or wherein the water injection platform comprises a monitor system for predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical bottom level and/or wherein the water injection platform comprises a pumping station on a dredging ship for pumping the sediment from the collector towards a dredging ship or a stationary pumping station for pumping the sediment from the collector towards a pipe line to relocate the sediment to a dumping or treatment site where the sediment is permanently stored or where it is re-suspended and carried away from the area temporally or permanently.
 49. A monitor system for assisting a dredging process in a navigation channel, the dredging process comprising a step of performing agitation for mobilizing sediment and displacing the mobilized sediment to a collector being a trench in the navigation channel wherein the trench has, when not being filled with sediment, a bottom level positioned substantially deeper than the nautical depth of the navigation channel and a separate step of, after solidification of the sediment collected in the collector, removing the solidified sediment from the collector so that the collector again has a bottom level positioned substantially deeper than the nautical depth of the navigation channel, the monitoring system being adapted for determining any of soil strength and/or density and determining based thereon any or more of the dredging power, the dredging effort, the water injection volume to erode, liquefy or mobilise the underwater sediment layer, and/or for predicting when the sediment needs to be removed from the collector for guaranteeing a predetermined nautical bottom level. 